Ibm uPD78082 Manual do Utilizador descarregar pdf (Página 203)

180

CHAPTER 12 INTERRUPT FUNCTION

(5) Program status word (PSW)

The program status word is a register to hold the instruction execution result and the current status for interrupt

request. The IE flag to set maskable interrupt enable/disable and the ISP flag to control multiple interrupt

processing are mapped.

Besides 8-bit unit read/write, this register can carry out operations with a bit manipulation instruction and

dedicated instructions (EI and DI). When a vectored interrupt request is acknowledged or when the BRK

instruction is executed, the contents of PSW is automatically saved to the stack and the IE flag is reset to 0.

If a maskable interrupt request is acknowledged the contents of the priority specify flag of the acknowledged

interrupt are transferred to the ISP flag. The contents of PSW are also saved to the stack by the PUSH PSW

instruction. It is reset from the stack with the RETI, RETB, and POP PSW instructions.

RESET input sets PSW to 02H.

Figure 12-7. Program Status Word Configuration

IEPSW

RBS1

RBS0

ISP

02H

State after

Reset

ISP

Used when normal instruction is executed

Priority of Interrupt Currently Being Received

High-priority interrupt servicing

(low-priority interrupt disable)

Interrupt not acknowledged or low-priority

interrupt request servicing

(all-maskable interrupts enable)

IE Interrupt Request Acknowledge Enable/Disable

0 Disable

1 Enable

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Ibm uPD78082 Manual do Utilizador Página 203